This invention covers a system and method for Electric-field (E-field) based projectile detection. The invention comprises an E-field sensor configuration and noise cancellation algorithm through which the system can determine the direction and speed of a projectile passing the sensors. The E-field based system can detect both supersonic and subsonic projectiles. The unique E-field signature from a projectile makes it feasible to detect multiple consecutive shots within a short time period (a few milliseconds). One embodiment includes a low-cost microphone, creating an acoustic-enabled E-field projectile detector with an improved detection rate and much lower false-alarm rate for supersonic projectiles than a detector based on E-field alone. Another embodiment combines an array of electric potential sensors and an array of microphones to form an E-field and acoustic bi-modal projectile detection system that utilizes the two orthogonal technologies to enhance the projectile detection capability. An additional embodiment is to add one or multiple electric potential sensors to an existing acoustic array-based projectile detection system to retrofit the system already built and reduce its false alarm rate.
There are various situations in which people such as military warfighters or law enforcement personnel need a real-time notification system to detect projectiles such as small-arms fire. Such a system might be free-standing, mounted on a person, or mounted on a vehicle. Projectiles, including bullets, passing through open-air regions carry an electric charge from the initial explosive combustion and triboelectric charging that occurs when the object passes through open-air regions. This charge can be sensed by an electric field (E-field) sensor or electric potential sensor. Current acoustic sensor based detection systems may become saturated or degraded by reverberation and multipath propagation, multiple threat scenarios, high levels of acoustic noise, and vibration on vehicles. In addition, acoustic sensing based systems do not work for subsonic or silenced projectiles such as gunshots. Also, acoustic-based systems have difficulties detecting multiple consecutive shots from a single or multiple shooters if these projectiles come in a very short period of time.